A vehicle may include a pressurized tank that holds fuel or some other gaseous substance that is used while the vehicle operates. For example, some vehicles operate using fuel supplied from a pressurized tank wherein the fuel is stored under pressure so a greater quantity of fuel may be stored in the tank. Downstream of the tank, a pressure regulator and valves are often included to reduce the pressurized gas to a more suitable pressure for introduction to the engine, and the pressurized gas may be introduced to an engine via delivery conduits including a manifold such as a fuel rail.
Because the gaseous contents of the storage tank are stored under pressure, a breach of the system to atmospheric pressure may result in a pressure differential producing a net flow of gaseous fuel from the storage tank to the region of the leak. For this reason, vehicles often include leak identification modes to enable the engine to continue operating when a fuel supply system incurs a significant leak in the system. One example is shown by U.S. Pat. No. 6,314,948 that describes a means of detecting the air rail pressure to determine whether a loss or significant reduction in the air pressure delivered to the fuel and air rails has occurred.
The inventors herein have recognized disadvantages with such approaches and developed a method for closing a tank valve in response to potential leaks in the gaseous fuel system. By comparing a tank pressure to one or more of a fuel rail pressure and a fuel line pressure, it is possible to detect leaks in the gaseous fuel system in a manner that allows accurate identification of degradation in the fuel system from the injector to the fuel tank while still enabling increased usage of gaseous fuel in the tank even at low pressures. Then, the method includes overriding the gaseous fuel supplying based on an overly high gaseous fuel tank pressure and an insufficient gaseous rail pressure and closing the storage tank valve in response to the detected leak when one or more of a fuel rail pressure or fuel line pressure falls below a lower threshold while a tank pressure is higher than an upper threshold.
In one particular example, based on a pressure difference between the tank and, for example, a high-pressure sensor in the fuel line being above a threshold, the method further includes closing the tank valve and switching the source of fuel. For example, a vehicle that operates on both gaseous and liquid fuels may switch from operating solely on a gaseous fuel to operating solely on a liquid fuel when a leak develops in the gaseous fuel system. If the engine were to continue operating while gaseous fuel was delivered from the storage tank, the engine might operate leaner than is desired because there might be an insufficient flow rate of fuel from the tank to the engine.
The present description may provide several advantages. In particular, the approach may be applicable to different types of fuel injection systems and gases. Further, the present description provides an operating mode based on the amount of fuel stored in order to reduce the loss of fuel. Therefore, the approach may reduce the amount of gaseous fuel that may be vented into the atmosphere if a leak develops in a gaseous fuel system. In addition, when no leaks are detected, the engine system functions as designed, and the system further allows for: solely supplying a gaseous fuel to an engine when a pressure of the gaseous fuel is greater than a threshold tank pressure; and supplying the gaseous fuel and a liquid fuel when the pressure of the gaseous fuel is less than the threshold tank pressure. By supplying liquid fuel and gaseous fuel to an engine when a pressure of a tank is less than a threshold tank pressure, it may be possible to draw additional gas from the storage tank while providing liquid fuel to the engine so that the engine does not misfire or operate richer than is desired. In this way, the gaseous fuel tank may be evacuated of a pressurized gas while the engine provides acceptable performance in a manner that extends the operating time or range of the vehicle and engine since the gaseous tank may be more completely evacuated.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.